US8659919B2 - Circuit to improve light load power factor of power supply - Google Patents

Circuit to improve light load power factor of power supply Download PDF

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US8659919B2
US8659919B2 US12/896,259 US89625910A US8659919B2 US 8659919 B2 US8659919 B2 US 8659919B2 US 89625910 A US89625910 A US 89625910A US 8659919 B2 US8659919 B2 US 8659919B2
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circuit
terminal
capacitor
light load
switching transistor
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US20110080144A1 (en
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Guichao Hua
Xiaoli Yao
Liangan Ge
Lijun REN
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THINKLUX (Zhejiang) Lighting Tech Co Ltd
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Inventronics Hangzhou Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/42—Circuits or arrangements for compensating for or adjusting power factor in converters or inverters
    • H02M1/4208—Arrangements for improving power factor of AC input
    • H02M1/4225—Arrangements for improving power factor of AC input using a non-isolated boost converter
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/007—Regulation of charging or discharging current or voltage
    • H02J7/0071—Regulation of charging or discharging current or voltage with a programmable schedule
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/02—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries for charging batteries from ac mains by converters
    • H02J7/04—Regulation of charging current or voltage
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/34—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering
    • H02J7/345—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering using capacitors as storage or buffering devices
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0003—Details of control, feedback or regulation circuits
    • H02M1/0032—Control circuits allowing low power mode operation, e.g. in standby mode
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B40/00—Technologies aiming at improving the efficiency of home appliances, e.g. induction cooking or efficient technologies for refrigerators, freezers or dish washers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P80/00—Climate change mitigation technologies for sector-wide applications
    • Y02P80/10—Efficient use of energy, e.g. using compressed air or pressurized fluid as energy carrier

Definitions

  • the present invention generally relates to a novel circuit which can improve the power factor of a power supply when experiencing a light load. Specifically, it relates to a circuit which can achieve a higher power factor even in a light load condition.
  • power factor correction technique is widely used in power electronics equipments.
  • a majority of the power factor correction (PFC) circuits can achieve higher power factor (PF) value in heavy load condition, but when the load reduces, the PF value will also decrease accordingly.
  • PF power factor
  • the PF value decreases more drastically when the load reduces in the high input voltage terminal.
  • electrical equipment with higher PF value is required in more occasions in which there is a wide load range. Therefore, techniques required to improve light load power factor for power supply are becoming important.
  • the present invention intends to solve the problems mentioned above which are related to the existing power factor correction circuits, and to provide a circuit which can provide higher PF value with light load.
  • a circuit to improve the power factor of a power supply at light load comprises a rectifier bridge, a filter positioned before or after the rectifier bridge, a logic control and power drive circuit, a switching transistor, a light load detecting circuit configured to output a control signal to the logic control and power drive circuit which controls the switching transistor to conduct when a heavy load is experienced and to cut off when a light load is experienced, in order to control the working status of the filter capacitor, and a power factor correction circuit.
  • FIG. 1 is a circuit which will improve light load power factor of power supply as applied in scheme (1) of the present invention.
  • FIG. 2 is a schematic circuit that can improve light load power factor of power supply based on scheme (2) of the present invention.
  • FIG. 3 is a schematic circuit that can improve light load power factor of power supply as suggested in scheme (3) of the present invention.
  • FIG. 4 is a schematic circuit of the first implementation which can improve light load power factor of power supply in scheme (1) of the present invention.
  • FIG. 5 is a schematic circuit of the second implementation which will improve light load power factor of power supply as in scheme (2) of the present invention.
  • FIG. 6 is a schematic circuit of the first implementation which can improve light load power factor of power supply as applied scheme (2) of the present invention.
  • FIG. 7 is a schematic circuit of the second implementation which is able to improve light load power factor of power supply as in scheme (2) of the present invention.
  • the problem mentioned above can be resolved with a filter capacitor at the input AC-side which can generate capacitive current which causes a phase difference between input voltage and input current, thus the PF value is reduced.
  • a filter capacitor at the DC side of the rectifier bridge is able to generate capacitive current, and it can also increase the current zero-crossing distortion of the PFC circuit, thus the PF value decreases.
  • a circuit which can improve the power factor of a power supply at light load comprises a filter, a light load detecting circuit, a logic control and power drive circuit, a switching transistor, a rectifier bridge and a power factor correction circuit.
  • the filter can be placed before or after the rectifier bridge and it contains at least one filter capacitor.
  • the light load detecting circuit outputs a control signal to the logic control and power drive circuit which controls the switching transistor to conduct at heavy load and to cut off at light load, thus, controlling the working status of the filter capacitor.
  • the circuit that can improve light load power factor of power supply comprises a capacitor, a light load detecting circuit, a switching transistor, a logic control and a power drive circuit, a rectifier bridge and a power factor correction circuit.
  • This circuit has the following features: the input terminals of the rectifier bridge are connected with the power line voltage, while the output of terminals of the rectifier bridge are connected in parallel with the power factor correction circuit and a branch circuit in which a capacitor and the switching transistor are connected in series.
  • the output of the light load detecting circuit is connected with the input of the logic control and power drive circuit, and the output of the logic control and power drive circuit is connected with the third terminal of the switching transistor.
  • the light load detecting circuit when the power supply is working in heavy load condition, the light load detecting circuit outputs control signal to logic control and power drive circuit which control the switching transistor to conduct; when the power supply is working in light load condition, the light load detecting circuit outputs control signal to logic control and power drive circuit which control the switching transistor to cut off.
  • the capacitor at the rectifier bridge' DC-side is worked as filter capacitor in heavy load, but will be cut off by switching resistor in light load.
  • the phase difference between input voltage and current in light load input is decreased, and so do the current zero-crossing distortion, thus the PF value is improved.
  • the circuit that can improve the power factor of a power supply at light load comprises a rectifier bridge, a first capacitor, a second capacitor, an inductor, a switching transistor, a logic control and power drive circuit, a light load detecting circuit and a power factor correction circuit.
  • This circuit has the following features: the two terminals of the power line voltage is connected with the input terminal of the rectifier bridge, while the positive output of the rectifier bridge is connected with one terminal of the inductor and one terminal of the first capacitor.
  • the other terminal of the inductor is connected with one terminal of the second capacitor and the positive input terminal of the power factor correction circuit, while the negative input terminal of the power factor correction circuit is connected to the ground.
  • the other terminal of the second capacitor is connected with the second terminal of the switching transistor, while the first terminal of the switching transistor is connected to the ground.
  • the output terminal of the light load detecting circuit is connected with the input terminal of the logic control and power drive circuit, and the output of the logic control and power drive circuit is connected with the third terminal of the switching transistor.
  • the light load detecting circuit when the power supply is working in a heavy load condition, the light load detecting circuit outputs the control signal to logic control and power drive circuit which signal the switching transistor (S 1 ) to conduct, capacitor Cx 1 , inductor L 1 and capacitor Cx 2 form ⁇ -shaped filter; when the power supply is working in a light load condition, the light load detecting circuit outputs the control signal to logic control and power drive circuit which signal the switching transistor (S 1 ) to cut off, and thus capacitor Cx 2 is opened, inductor L 1 and inductor L 2 are connected in series, and work as a part of the energy inductor in Boost power factor correction circuit.
  • scheme (2) the capacitor and inductor at the DC-side of the rectifier bridges working as a ⁇ -shaped filter in heavy load. While in light load, the last stage filter capacitor of the ⁇ -shaped filter is cut off by switching resistor, decreasing the phase difference between input voltage and the current zero-crossing distortion, and thus the PF value can be improved. Meanwhile, when the capacitor is cut off from the circuit, the inductor of the ⁇ -shaped filter is connected in series with the energy inductor of the followed Boost PFC circuit, increasing the energy inductance of Boost PFC circuit, but decreasing the current zero-crossing distortion, and thus the PF value of the power supply can be further improved. Therefore, when compared with scheme (1), scheme (2) can improve light load power factor of power supply more effectively.
  • the circuit that can improve light load power factor of power supply comprises a rectifier bridge (BD 1 ), a capacitor (Cx 1 ), a switching transistor (S 1 ), a logic control and power drive circuit, a light load detecting circuit and a power factor correction circuit.
  • BD 1 rectifier bridge
  • Cx 1 capacitor
  • S 1 switching transistor
  • the filter is a capacitor (Cx 1 ), which is connected in series with a switching transistor (S 1 ) and constitute a series loop, then the two terminals of the series loop are connected parallel to the power line, and also to the rectifier bridge, the output terminals of the rectifier bridge are connected with the power factor correction circuit, and the output terminal of the light load detecting circuit is connected to the input of the logic control and power drive circuit, while the output of the logic control and power drive circuit is connected with the third terminal of the switching transistor.
  • the filter is a capacitor (Cx 1 ), which is connected in series with a switching transistor (S 1 ) and constitute a series loop, then the two terminals of the series loop are connected parallel to the power line, and also to the rectifier bridge, the output terminals of the rectifier bridge are connected with the power factor correction circuit, and the output terminal of the light load detecting circuit is connected to the input of the logic control and power drive circuit, while the output of the logic control and power drive circuit is connected with the third terminal of the switching transistor.
  • the light load detecting circuit when the power supply is working in a heavy load condition, the light load detecting circuit outputs the control signal to logic control and power drive circuit which signals the switching transistor S 1 to conduct; when the power supply is working in a light load condition, the light load detecting circuit outputs the control signal to logic control and power drive circuit which signals the switching transistor S 1 to cut off.
  • the filter capacitor at AC input side is cut off by switching resistor in light load decreasing the phase difference between input voltage and current, and thus improving the PF value at a light load power supply.
  • the light load detecting circuit in the present invention comprises of the detection of input power, and/or detection of output power, and/or detection of any signals which controlling the output power.
  • FIG. 1 is an implementation of the circuit disclosed with respect to scheme (1) which can improve light load power factor of a power supply.
  • the circuit comprises a power line voltage, a capacitor Cx 1 , a light load detecting circuit 12 , a switching transistor (S 1 ), a logic control and a power drive circuit 14 , a rectifier bridge DB 1 and a power factor correction circuit 16 .
  • This circuit has the following features: the input terminal of the rectifier bridge BD 1 is connected to the power line voltage 10 , the capacitor Cx 1 and the switching transistor (S 1 ) are connected in series, which are connected in parallel with an output terminal of the rectifier bridge BD 1 and the power factor correction circuit 16 , Vo act as output voltage of the power factor correction circuit 16 .
  • the output of the light load detecting circuit 12 is connected to the input of the logic control and power drive circuit 14 , while the output of the logic control and power drive circuit 14 is connected to the third terminal of the switching transistor S 1 .
  • FIG. 2 is the implementation of a circuit suggested in scheme (2) which can improve light load power factor of power supply.
  • This circuit comprises a power line voltage 10 , a rectifier bridge BD 1 , a first capacitor Cx 1 , a second capacitor Cx 2 , an inductor L 1 , a switching transistor S 1 , a logic control and a power drive circuit 14 , a light load detecting circuit 12 , and a power factor correction circuit 16 .
  • This circuit has the following features: the power line voltage 10 is connected to the input terminal of the rectifier bridge BD 1 , the positive output of the rectifier bridge BD 1 is connected to one terminal of the inductor L 1 and one terminal of the first capacitor Cx 1 , while the another terminal of the inductor L 1 is connected to one terminal of the second capacitor Cx 2 and the positive input of the power factor correction circuit 16 .
  • the negative input of the power factor correction circuit 16 is connected to ground 18
  • the other terminal of the second capacitor Cx 2 is connected to the second terminal 2 of the switching transistor (S 1 ).
  • the output of the light load detecting circuit 12 is connected to the input of the logic control and power drive circuit 14
  • the output of the logic control and power drive circuit 14 is connected to the third terminal 3 of the switching transistor (S 1 ).
  • Vo is the output voltage of the power factor correction circuit 16 .
  • FIG. 3 is the implementation of a circuit as described in scheme (3) which can improve light load power factor of power supply.
  • This circuit comprises a power line voltage 10 , a capacitor Cx 1 , a switching transistor (S 1 ), a rectifier bridge BD 1 ⁇ a logic control and a power drive circuit 14 , a light load detecting circuit 12 and a power factor correction circuit 16 .
  • This circuit has the following features: the filter capacitor Cx 1 is connected in a series with the switching transistor ⁇ S 1 ⁇ , then they are connected in parallel with the power line voltage 10 and followed by the rectifier bridge BD 1 , the output of the rectifier bridge BD 1 is connected to the power factor correction circuit 16 .
  • Vo is the output voltage of the power factor correction circuit.
  • the output of the light load detecting circuit 12 is connected to the input of the logic control and power drive circuit 14 , and the output of the logic control and power drive circuit 14 is connected to the third terminal 3 of the switching transistor S 1 .
  • FIG. 4 is a detailed implementation of the circuit which can improve light load power factor of power supply as described in scheme (1).
  • the power factor correction circuit 16 comprises an inductor L 1 , a MOSFET Q 1 , a diode D 1 , an electrolytic capacitor C 1 , a resistors R 1 and R 2 , a second capacitor C 2 and a PFC controller 20 .
  • the logic control and power drive circuit 14 together with the light load detecting circuit 12 are combined into a control circuit 22 .
  • the power line voltage 10 is connected to the input terminal of rectifier bridge BD 1 , the positive output of the rectifier bridge BD 1 is connected to one terminal of inductor L 1 and one terminal of capacitor Cx 1 , the negative output of the rectifier bridge BD 1 is connected to the ground 18 , the other terminal of capacitor Cx 1 is connected to the second terminal 2 of switching transistor (S 1 ), the first terminal 1 of switching transistor (S 1 ) is connected to the ground 18 , the other terminal of inductor L 1 is connected with the drain of MOSFET Q 1 and the anode of diode D 1 , the source of MOSFET Q 1 is connected to one terminal of resistor R 2 , and the another terminal of R 2 is connected to the ground 18 .
  • the output of the PFC controller 20 is connected to the gate of MOSFET Q 1 and one terminal of resistor R 1 , the another terminal of resistor R 1 is connected to one terminal of the second capacitor C 2 and the input terminal of the control circuit 22 , and the output terminal of the control circuit 22 is connected with the third terminal 3 of switching transistor (S 1 ).
  • the cathode of diode D 1 is connected to the positive terminal of electrolytic capacitor C 1 , the negative terminal of electrolytic capacitor C 1 is connected to the ground 18 , and the voltage of the electrolytic capacitor C 1 is the output voltage Vo.
  • the signals driven by gate of MOSFET Q 1 are sampled and filtered by resistor R 1 and second capacitor C 2 into voltage signals, received by the control circuit 22 and output control signals to the third terminal 3 of switching resistor (S 1 ) in order to control the switching action of S 1 .
  • the control circuit 22 processes voltage signals produced by resistor R 1 and second capacitor C 2 , and output high level signals causing switching transistor to conduct, then capacitor Cx 1 is worked as a filter capacitor.
  • the control circuit 22 processes voltage signals produced by resistor R 1 and second capacitor C 2 , and output low level signals causing switching transistor to cut off, then when capacitor Cx 1 is bypassed and light load power factor can be improved.
  • FIG. 5 is another exemplary implementation of the circuit in details which can improve light load power factor of power supply described in scheme (1).
  • the power factor correction circuit comprises an inductor L 1 , a MOSFET Q 1 , a diode D 1 , an electrolytic capacitor C 1 , a resistors R 1 and R 2 , a second capacitor C 2 , and PFC controller 20 .
  • the logic control and power drive circuit 14 together with the light load detecting circuit 12 are combined into the control circuit 22 .
  • the power line voltage 10 is connected to the input terminal of rectifier bridge BD 1 , the positive output of rectifier bridge BD 1 is connected to one terminal of inductor L 1 and one terminal of capacitor Cx 1 , while the negative output of rectifier bridge BD 1 is connected to the ground 18 , the other terminal of capacitor Cx 1 is connected to the second terminal 2 of switching transistor (S 1 ), and the first terminal 1 of switching transistor (S 1 ) is connected to the ground 18 .
  • Another terminal of inductor L 1 is connected to the drain of MOSFET Q 1 and the anode of diode D 1 , the source of MOSFET Q 1 is connected to one terminal of resistor R 2 and one terminal of resistor R 1 , the another terminal of R 2 is connected to the ground 18 , and the output of PFC controller 20 is connected to the gate of MOSFET Q 1 .
  • Another terminal of resistor R 1 is connected to one terminal of capacitor C 2 and the input terminal of the control circuit 22 , while the output terminal of the control circuit 22 is connected to the third terminal 3 of switching transistor (S 1 ).
  • the cathode of diode D 1 is connected to the positive terminal of electrolytic capacitor C 1 , the negative terminal of electrolytic capacitor C 1 is connected to the ground 18 , and the voltage of the electrolytic capacitor C 1 is the output voltage Vo.
  • the current signals of MOSFET Q 1 are detected by resistor R 2 then is sampled and filtered by resistor R 1 and second capacitor C 2 into voltage signal which then received by the control circuit 22 and output control signals to the third terminal 3 of switching resistor (S 1 ) to control the switching action of S 1 .
  • the control circuit 22 processes the voltage signals produced by resistor R 1 and second capacitor C 2 , and output high level signal which triggers switching transistor to conduct, then capacitor Cx 1 is worked as a filter capacitor.
  • the control circuit processes the voltage signals produced by resistor R 1 and second capacitor C 2 , and output low level signal which cause switching transistor to cut off, capacitor Cx 1 is therefore bypassed and light load power factor is improved.
  • FIG. 6 is an exemplary implementation of a circuit which can improve light load power factor of power supply described in scheme (2).
  • the power factor correction circuit 16 comprising an inductor L 2 , a MOSFET Q 1 , a diode D 1 , an electrolytic capacitor C 1 , a resistors R 1 and R 2 , a second capacitor C 2 , and a PFC controller 20 .
  • the logic control and power drive circuit 14 together with the light load detecting circuit 12 are combined into the control circuit 22 .
  • the power line voltage 10 is connected with the input terminal of rectifier bridge BD 1 , the output terminal of rectifier bridge BD 1 is connected to Cx 1 , the positive output of rectifier bridge BD 1 is connected to one terminal of inductor L 1 , the negative output of rectifier bridge BD 1 is connected to the ground 18 , the another terminal of inductor L 1 is connected to one terminal of capacitor Cx 2 and one terminal of inductor L 2 , and the another terminal of capacitor Cx 2 is connected to the second terminal 2 of switching transistor (S 1 ).
  • the first terminal 1 of switching transistor 51 is connected to the ground 18 , the another terminal of inductor L 2 is connected with to drain of MOSFET Q 1 and the anode of diode D 1 , the source of MOSFET Q 1 is connected to one terminal of resistor R 2 , and the another terminal of R 2 is connected to the ground 18 .
  • the output of PFC controller 2 o is connected to the gate of MOSFET Q 1 and one terminal of resistor R 1 , the another terminal of resistor R 1 is connected to one terminal of second capacitor C 2 and the input terminal of control circuit 22 , and the output terminal of control circuit 22 is connected with the third terminal 3 of switching transistor (S 1 ).
  • the cathode of diode D 1 is connected to the positive terminal of electrolytic capacitor C 1 , the negative terminal of electrolytic capacitor C 1 is connected to the ground 18 , and the voltage of the electrolytic capacitor C 1 is the output voltage Vo.
  • the signals driven by gate of MOSFET Q 1 is sampled and filtered by resistor R 1 and capacitor C 2 into voltage signal, and then received by the control circuit 22 and output control signals to the third terminal 3 of switching resistor (S 1 ) to control switching action of (S 1 ).
  • the control circuit 22 processes voltage signals produced by resistor R 1 and second capacitor C 2 , and output high level signals which cause switching transistor to conduct, then capacitor Cx 2 is worked as a filter capacitor.
  • the control circuit When the circuit is operated in a light load condition, the control circuit processes voltage signals produced by resistor R 1 and capacitor C 2 , and output low level signal causing the switching transistor S 1 to cut off, then capacitor Cx 2 is bypassed, inductor L 1 and inductor L 2 are connected in series and worked as an energy inductor of the PFC circuit, light load power factor can then be improved.
  • FIG. 7 is another exemplary implementation of the circuit which can improve light load power factor of power supply as described in scheme (2).
  • the power factor correction circuit 16 comprises an inductor L 2 , a MOSFET Q 1 , a diode D 1 , an electrolytic capacitor C 1 , resistors R 1 and R 2 , a second capacitor C 2 and a PFC controller 20 .
  • the logic control and power drive circuit 14 together with the light load detecting circuit 12 are combined into the control circuit 22 .
  • the power line voltage 10 is connected to the input terminal of rectifier bridge BD 1 , the output terminal of rectifier bridge BD 1 is connected to Cx 1 , the positive output of rectifier bridge BD 1 is connected to one terminal of inductor L 1 , and the negative output of rectifier bridge BD 1 is connected to the ground 18 .
  • the other terminal of capacitor Cx 1 is connected to the ground 18 , the another terminal of inductor L 1 is connected to one terminal of capacitor Cx 2 and one terminal of inductor L 2 , another terminal of capacitor Cx 2 is connected to the second terminal 2 of switching transistor (S 1 ), and the first terminal of switching transistor S 1 is connected to the ground 18 .
  • Another terminal of inductor L 2 is connected to the drain of MOSFET Q 1 and the anode of diode D 1 , the source of MOSFET Q 1 is connected to one terminal of resistor R 2 and one terminal of resistor R 1 , and another terminal of R 2 is connected to the ground 18 .
  • the output of PFC controller 20 is connected to the gate of MOSFET Q 1 , another terminal of resistor R 1 is connected to one terminal of second capacitor C 2 and the input terminal of control circuit 22 , the output terminal of the control circuit 22 is connected to the third terminal 3 of switching transistor (S 1 ), and the cathode of diode D 1 is connected to the positive terminal of electrolytic capacitor C 1 .
  • the negative terminal of electrolytic capacitor C 1 is connected to the ground, and the voltage of the electrolytic capacitor C 1 is the output voltage Vo.
  • the current signals of MOSFET Q 1 detected by resistor R 2 is sampled and filtered by resistor R 1 and second capacitor C 2 into voltage signal, which will received by the control circuit 22 and output control signals to the third terminal 3 of switching resistor S 1 to control the switching action of S 1 .
  • the control circuit 22 processes voltage signals produced by resistor R 1 and capacitor C 2 , consequently output high level signals which will cause switching transistor to conduct, then capacitor Cx 2 is worked as a filter capacitor.
  • the control circuit 22 processes voltage signals produced by resistor R 1 and capacitor C 2 , which then output low level signals causing switching transistor to cut off, capacitor Cx 2 is therefore bypassed.
  • Inductor L 1 and inductor L 2 are connected in series and work as an energy inductor of PFC circuit 16 , hence light load power factor can be improved.

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  • Power Engineering (AREA)
  • Rectifiers (AREA)
  • Dc-Dc Converters (AREA)
US12/896,259 2009-10-01 2010-10-01 Circuit to improve light load power factor of power supply Expired - Fee Related US8659919B2 (en)

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CN200910153406A CN101674004B (zh) 2009-10-01 2009-10-01 一种提高电源轻载功率因数的电路
CN200910153406 2009-10-01
CN200910153406.2 2009-10-01

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Cited By (3)

* Cited by examiner, † Cited by third party
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US20140126253A1 (en) * 2011-07-20 2014-05-08 Hewlwtt-Packard Development Company, L.P. Power supply system with dynamic filtering
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